From William Candillon today on the "Yet another PHP blog", there's his comparison at the source coude level of PHPCompiler versus Yaxx.

Before I choose yaxx and XML tools for code source transformation, I looked very attentively the phpCompiler project.

The main goal of phpCompiler is to translate PHP code directly into Linux assembly code (and they are apparently very close to it).

He mentions, though, that phpCompiler just doesn't fit what he's trying to do. He needs things like portability between platforms and a simple way to extend the PHP lexer and grammer for phpAspect. Unfortunately, phpCompiler either doesn't allow these or just makes them too difficult. He makes his choice for his situation - Yaxx

In his new post on "Yet Another PHP Blog" (a blog documenting his participation in Google's Summer of Code), William Candillon talks about some issues he had when working on his aspect-oriented framework.

The original PHP compiler doesn't use AST representation of a source code so in the previous versions of phpAspect I had to fill the php grammar with my own AST constructions. It was a painful job and moreover I had to do it in each major version of PHP. For this new version, I'm using the yaxx project written by Dr. Yijun Yu. The yaxx tool is a yacc skeleton which build an xml ast representation of a source code according to his grammar.

He includes two images, one showing the simple class code and the other showing the tree that's obtained from the XML generated by the yaxx tool for that class structure.